docs: def info(gandi, resource, ip):
      """Display information about a vlan."""
      output_keys = ['name', 'state', 'dc', 'subnet', 'gateway']
  
      datacenters = gandi.datacenter.list()
  
      vlan = gandi.vlan.info(resource)
  
      gateway = vlan['gateway']
      if not ip:
          output_vlan(gandi, vlan, datacenters, output_keys, justify=11)
          return vlan
  
      gateway_exists = False
  
      vms = dict([(vm_['id'], vm_) for vm_ in gandi.iaas.list()])
      ifaces = gandi.vlan.ifaces(resource)
  
      for iface in ifaces:
          for ip in iface['ips']:
              if gateway == ip['ip']:
                  gateway_exists = True
  
      if gateway_exists:
          vlan.pop('gateway')
      else:
          vlan['gateway'] = ("%s don't exists" % gateway if gateway
                             else 'none')
  
      output_vlan(gandi, vlan, datacenters, output_keys, justify=11)
  
      output_keys = ['vm', 'bandwidth']
      for iface in ifaces:
          gandi.separator_line()
          output_iface(gandi, iface, datacenters, vms, output_keys,
                       justify=11)
          for ip in iface['ips']:
              output_ip(gandi, ip, None, None, None, ['ip'])
              if gateway == ip['ip']:
                  output_line(gandi, 'gateway', 'true', justify=11)
  
      return vlan